Screen printing machines are industrially used to decorate large flat surfaces, such as for example pieces of fabric or paper. This type of machine, due to its working efficiency and the speed with which it operates, has in many cases replaced the machines which by other means have conventionally been used for printing.
The great technological evolution of screen printing machines, up to the time of achieving their present efficiency, has been possible due to an uninterrupted succession of improvements.
Machines of this type mainly consist of a carriage which travels on guides, describing a rectilineal path on a table whereon the piece to be processed is spread and immobilized.
The piece to be processed is spread and fixed on a long table on which a carriage, guided throughout its travel, slides. Such carriage supports the printing screen and the elements necessary to spread the screen printing inks which, through the screen, produce the decorative patterns on the piece being printed.
The carriage travels along the piece advancing in a single operative direction until the entire piece has been decorated.
The screen printing ink which impregnates the piece to be printed, thus producing the designs composing the decorative patterns, is spread in the interior of the screen.
Since a separate screen is needed to apply each one of the colors which adorn the piece, the machine will make as many movements or productive passes on the piece to be printed as the number of different colors to be applied to the piece.
The screen is lowered at each stop and is superficially coupled to the piece to be printed. Once the screen printing ink is spread, the screen is raised and thus separated from the piece, and the carriage is advanced to another station.
Heretofore, spreading of the ink has been achieved by means of an arm which, provided with a squeegee or stripper, makes a tracking movement, thus spreading the ink over the screen and through the perforations therein.
Since an unproductive return movement is necessary with each productive printing movement, and since each productive printing movement comprises a plurality of screen processing application stops or stations, it is understood that one of the most important factors of the production yield of such machines is the speed with which the machine travels.
On the other hand, bearing in mind that one of the restrictions on the velocity of screen printing, and therefore on the yield of the machine involves the dimensions of the screen, it will also be understood that manufacturers always attempt to increase the size of the screen carriers used in their machines. However, when the dimensions of the screen are increased, the arm bearing the squeegee or stripper becomes in turn so supersized that its working efficiency is remarkably reduced, to such an extent that the inferior quality of the printed pieces is not permissible.
Just as important as the above mentioned factors on the yield of the machine, is the driving speed of the screen printing application means and the dimensions of the screen.
The automatic mechanisms which cause the carriage to travel and the devices used for screen printing application have been so improved that the working speeds thereof have reached their maximum.
The dimensions of the screen are determined by the width of the piece and the length of the pitch or repetition of the design.
The screens have heretofore covered a surface which comprises the width of the piece and a pitch or a complete portion of the design constituting the pattern with which the piece is decorated.
According to the above, it can be seen that the screen can be supersized only in a single direction, since the width of the piece determines the other, which is invariable. Consequently, the screen can only be supersized by increasing its length, which corresponds to the direction of the warp of the piece. However, this increase should, as a minimum, comprise a complete unit or a pitch of the design, whereby a new screen, which would be double or triple the size of a conventional screen would be obtained.
On increasing the dimensions of the screen, lengthening it in the direction of the warp, the application stops or stations are reduced to a half, a third or a quarter, according to the rate of increase, whereby the unproductive intervals of the machine are partially reduced.
A screen having the described features should be stronger than the conventional, since it will be heavier and would require strong and efficient movement producing members, in order to maintain the same working speed.
On the other hand, the means used to spread the printing ink, which in a conventional screen operates in the direction of the weft of the piece, since this is the largest part of the frame, cannot in the new screen operate in the same direction, since the smallest part of the new screen corresponds precisely to the largest part of the other. Consequently, the size, weight and characteristics of the spreading means as well as the strength and weight of the mechanisms operating the same, are greater than in a conventional machine.
All these conditions prevent the occasional modification of a conventional machine, to such an extent that even though its function is identical and the principle by which it develops is maintained constant, the machine evolves and is improved in such a way that it is different.